Quantifying the Effects of Aerogels for Their Use in Catalytic Converters

Aerogel catalysts are being investigated to improve performance, reduce cost, and reduce the environmental impact of automotive catalytic converters. Catalytic converters are an expensive but necessary technology incorporated in gas-powered vehicle emissions systems. These devices use large amounts of expensive materials called Platinum Group Metals (PGMs) which catalyze the oxidation and reduction reactions of harmful pollutants in engine emissions. To improve this technology, PGM concentrations and light-off temperatures should be decreased. The light-off temperature is the temperature at which catalytic converters start converting 50% of a specific pollutant. Aerogels are of interest for application in catalytic converters because of their extremely high porosity and surface area. By incorporating PGMs into aerogel materials, comparable light-off temperatures to products on the market have been achieved with smaller concentrations of PGMs. Because of these results, the next step is to isolate aerogel’s unique qualities to quantify their effects on catalytic performance. To do this, two chemically identical but structurally different catalytic materials have been made and then tested to find the differences in light-off temperatures. These two catalysts differ from each other in one way: one catalyst is aerogel material and one is a non-aerogel material called xerogel. The testing of these materials is done using the Union College Aerogel Testbed (UCAT) which subjects the samples to realistic automotive conditions using CLEERS (an automotive industry professional organization dedicated to pollution mitigation research) guidelines. Despite the difference in physical properties between the aerogels and xerogels, the experiment is designed so that each sample tested in the UCAT has the same volume and contains the same total mass amount of PGMs (i.e. catalytically active material). Two sets of aerogel and xerogel samples were made using two different PGMs of interest. Palladium alumina (PdAl) samples were made using 11.6 mg of palladium in each of the aerogel and xerogel samples. Rhodium alumina (RhAl) samples were made using 11.4 mg of rhodium in each of the aerogel and xerogel samples. Comparing the aerogel PdAl sample to the xerogel PdAl sample, the light-off temperature of hydrocarbons (HCs) was improved by 50℃, and carbon monoxide (CO) was improved by over 25℃. Comparing the aerogel to xerogel RhAl samples, the light-off temperature for nitrogen oxides (NOx) was also improved by over 25℃. These results indicate that aerogel materials improve catalytic efficiency.